Conventionally, a technique for etching a multilayer film formed on a target object has been known. For example, there is disclosed a technique of etching an amorphous carbon film by a plasma of a sulfur-containing gas using, as a mask, an SiON film having a predetermined pattern formed on the target object, and etching a silicon oxide film by a plasma of a CF-based gas using the amorphous carbon film as a mask (see, e.g., Japanese Patent Application Publication No. 2011-216644).
However, in the conventional technique, since the roughness of the amorphous carbon film due to etching is transferred to the underlying silicon oxide film, the lines formed by etching may be roughened, or the cross-sectional shape of the lines may be deteriorated.
For example, in the conventional technique, when etching a silicon oxide film without supplying a high frequency bias power, the cross-sectional shape of the lines formed by etching may be tapered. Meanwhile, in the conventional technique, when etching the silicon oxide film while supplying a high frequency bias power, wiggling of lines formed by etching may occur.